Apparatus and method for shrinking plastic sheet material about stacked goods

ABSTRACT

Forced-draft gas burners mounted on a support in vertically offset relationship discharge respective streams of combustion gases against a stack of goods loosely enveloped in a bag of heat-shrinkable plastic sheet material. To reach all sides of the stack, the support may be mounted on a wheeled carriage and moved around the stack, or the stack may be moved on a turntable relative to the stationary support. The top of the stack may be reached by combustion gases from a separate, downwardly directed burner or by gases originating in burner units directed against the side of the stack and deflected toward the top by an adjustable hood.

United States Patent Ahrendt et a1.

APPARATUS AND METHOD FOR SHRINKING PLASTIC SHEET MATERIAL ABOUT STACKED GOODS Inventors: Heinrich Ahrendt,

Monchengladbachllehn; Karl Birkendahl, Niederkruchten-Elmpt, both of Germany Ahrendt & Birkendahl oHG, Monchengladbach-Hehn, Germany Filed: Oct. 24, 1972 Appl. No.: 299,115

Assignee:

Foreign Application Priority Data Oct. 25, 1971 Germany P 2153 001.8

US. Cl 432/5, 34/223, 432/124 Int. Cl. F271! 9/14 Field of Search 432/124, 222, 220;

References Cited UNITED STATES PATENTS 6/1944 Campbell 34/218 X DEC. 11, 1973 2,443,618 6/1948 Elden 34/218 x 2,588,728 3/1952 Hundstad 432/222 x 2,787,814 4/1957 Milligan........ 432/124 x 3,427,729 2/1969 Piazze 34/223 3,711,957 1/1973 Carver 34/223 Primary Examiner.lohn J. Camby Att0rney-Kurt Kelman et al.

[57] ABSTRACT Forced-draft gas burners mounted on a support in vertically offset relationship discharge respective streams 11 Claims, 8 Drawing Figures PATENTED DEC! 1 I973 SHEET 1 0F 4 b dmbm FIG.2

PATENTED DEC] 1 I973 menu APPARATUS AND METHOD FOR SHRINKING PLASTIC SHEET MATERIAL ABOUT STACKED GOODS This invention relates to the wrapping of stacked goods in heat-shrinkable plastic sheet material, and particularly to an apparatus and a method for tightening a heat-shrinkable plastic sheet about stacked goods.

It is common practice to stack individual pieces of material, such as bricks, or individual packages, such as cans of food, or pallets, loosely wrap the stack and the sides of the pallet in heatshrinkable, plastic sheet material, and to pass the wrapped stack and pallet through an oven or an arch carrying infrared lamps to heat and thereby shrink the enveloping sheet material into conforming engagement with the stack and pallet. The individual pieces or packages are consolidated into a coherent mass which is firmly anchored to the pallet by the shrunken plastic.

The known devices, if reasonably low in first cost and operating cost, are not very efficient and slow, and known devices which can shrink plastic envelopes on stack goods at a high rate are expensive to build and operate.

It is a primary object of this invention to provide relatively inexpensive apparatus for shrinking a plastic envelope on stacked goods, with or without a pallet, at a high rate and at low operating cost. It is another object to provide a method of operating such apparatus.

With these objects and others in view, as will presently become apparent, the apparatus of the invention includes a plurality of burner units mounted on a vertically extending support in vertically offset relationship, each burner unit including a mixing chamber, a combustion tube having an axis, an open axial end and another axial end communicating with the mixing cham her. A motor-driven blower draws atmospheric air into the mixing chamber, and a spark plug permits the gas in the chamber to be ignited. The axes of the combustion tubes of the burner units extend substantially in a common direction. A source ofa combustible gas communicates with the mixing chamber.

The burner units operate most efficiently when the axes of the combustion tubes are inclined 30 i relative to the horizontal, the open end of each tube being downwardly offset from the other axial end. One or more of the units may be guided movably on the support in the common direction of the associated combustion tubes. A hood may be provided for deflecting some of the combustion gases toward the top surface of a plastic-wrapped stack of goods. If the gas supply to individual burner units can be controlled, the units may also be employed for blowing cooling air against a previously heat-shrunk, soft plastic envelope.

When the support of the several burner units is mounted on a wheeled carriage, which may also support the source of combustible gas, a sheet of heatshrinkable plastic may be tightened about goods loosely enveloped by the sheet by wheeling the apparatus about the enveloped goods while burning the gas with the atmospheric air in each of the combustion tubes, and discharging the hot combustion gases so produced against the sheet.

Other features, addition objects, and many of the attendant advantages of this invention will readily become apparent from the following detailed description of preferred embodiments when considered-in connection with the appended drawing in which:

FIG. 1 shows apparatus of the invention in side elevation, portions of a housing being broken away to reveal internal structure;

FIG. 2 shows the apparatus of FIG. 1 in rear elevation and including auxiliary equipment;

FIG. 3 illustrates a modified apparatus of the invention and a stack of goods enveloped in a plastic sheet in a view analogous to that of FIG. 2;

FIG. 4 shows a further modification of the apparatus of FIG. 3 in a corresponding view;

FIG. 5 shows elements of the apparatus of FIG. 6 in rear elevation;

FIG. 6 is a top plan view of yet another embodiment of the invention including apparatus of the type shown in FIG. 1;

FIG. 7 shows the elements illustrated in FIG. 5 and associated devices of the apparatus of FIG. 6 in side elevation; and

FIG. 8 is an enlarged, sectional view of one of the burner units common to the several embodiments of the invention.

Referring now to the drawing in detail, and initially to FIG. 1, there is shown a burner column 1 essentially consisting of a housing 2 having the shape of a rectangular slab standing on one of its narrow, shorter sides and of six identical burner units 3, 4, 5 for which the housing 2 serves as a carrier or support. The burner unit 4 is arranged in its own housing 4' attached to the lower end of the housing 2 in such a manner that the unit 4 is horizontally offset from the lowermost burner unit 5 in the housing 2, the other four burner units 3 in the housing 2 being vertically offset from the unit 5 and from each other.

The housing or carrier 2 is pivotally mounted on a carriage 8 having four castor wheels 9 by means of. a horizontal shaft 7 and may be secured in a desired angular position by meansof a latch 6, not shown in detail. The carriage 8 has a frame 15 normally hidden by a shell 11 of glass-fiber reinforced polyester resin and supported by the wheels 9. A control panel 12 on the shell 11 faces on operator standing behind a handle bar 10 by means of which the entire apparatus may be wheeled about.

The space 13 in the shell 11 is accessible through a door, broken away in the view of FIG. 1, and encloses an electric storage battery 14 and a bottle 18 of liquefled propane gas. A shut-off valve 19, apressurereducing valve 20, and a flexible hose 2] lead from the bottle 18 to a manifold and to seven individual solenoid valves in the housing 2, not explicitly shown in FIG. 1, of which six connect the bottle 18 to respective burner units 3, 4, 5. The solenoid valves are controlled by a row of push button switches 16 on the control panel 12, and another row of switches 17 on the panel 12 control blower motors in the several blower units.

One of the blower units is shown in section in FIG. 8. It has a mixing chamber which is connected to the gas bottle 18, not itself seen in FIG. 8, by a solenoid valve 51. A cylindrical stainless steel combustion tube 52 communicates at one axial end with the chamber 50 and is spacedly and coaxially enveloped by a cooling jacket 53. The other axial end of the tube 52 is open to the atmosphere. Radial apertures 54 in the jacket 53 near the axially open end of the tube 52 provide an inlet for air which is drawn into the jacket 53 and into the chamber 50 by a blower 55 driven by an electric motort56. A spark plug 57 is provided in the chamber 50. The solenoid valve 51, the motor 56, and the spark plug 57 are connected to the battery 14 through associated switches 16, 17 and an operator-controlled ignition circuit, conventional in itself and not shown, all necessary conductors being combined in a cable 22 which leads from the housing 2 to the panel 12.

During normal operation of each burner unit, propane and atmospheric air are mixed in the chamber 50, the fuel mixture is ignited by the spark plug 67, and ignition takes place in the tube 52 whose wall is cooled by the air of combustion flowing through the jacket 53. The valve 20 and the blower speed are selected in such a manner that combustion is confined to the tube 52, and no flames emerge from the open end of the tube 52, only a stream of combustion gases having an initial temperature of about 750C.

As is shown in FIG. 2, the apparatus of FIG. 1 may be equipped with an auxiliary burner unit 26 adjustably secured to the housing or carrier 2. An upright, threaded spindle 23 is releasably attached to the top face of the housing 2. A nut 27 may be raised or lowered on the spindle 23 by turning a handwheel 28 on the nut. A circular, circumferential groove in the nut 27 is movably engaged by a ring at one end of an arm 24 whose other end carries the burner unit 26. The unit 26 is connected with the bottle 28 through the aforementioned seventh solenoid valve and with the battery 14 in a manner not explicitly shown, but obvious from the preceding description of FIGS. 1 and 8.

The arm 24 may turn on the nut 27 as a unit. The arm has two longitudinal parts connected by a pivot 25 which permits the burner unit 26 to be moved toward and away from the spindle 23. The axis of the combustion tube in the unit 26, identical with the unit illustrated in FIG. 8, is approximately vertical while the corresponding axes of the burner units 3, 4, extend in a common, approximately horizontal direction perpendicular to the axis of the shaft 7. The level of the unit 26 above ground, that is, a plane tangential to the four wheels 9, is approximately two meters and sufficient to accommodate the highest pallet about which an enveloping plastic sheet is to be shrunk.

The modified apparatus illustrated in FIG. 3 is identical with that described with reference to FIGS. 1 and 2 except as specifically stated hereinbelow. Its burner column 1' employs a carrier 35 which does not enclose the six burner units 3. The units are mounted on the rear face of the carrier 35 in such a manner that the axes of their combustion tubes are inclined relative to the horizontal at an angle of 30 i The column 1' is somewhat higher than the column 1 described above so that an auxiliary burner unit 26 is not required for work on a pallet loaded to the usual maximum height of 2 meters.

The pallet 32 shown in FIG. 3 is stacked with packages 33 which are loosely enveloped by a downwardly open bag 34 of heat-shrinkable plastic sheet material, as is known in itself. The vertical length of the bag is sufficient to extend downward below the loading platform of the pallet 32.

An upright cylindrical bar 31 is spacedly attached to the front face of the carrier 35. A downwardly open hood 29 is mounted on the bar 31 by means of a releasable clamp 30, conventional in itself and not shown in detail, so that the hood may be swung horizontally into and out of the illustrated position in which it is located in front of the discharge orifice of the topmost burner unit 3. The dimensions of the hood 29 and the vertical spacing or offset of the several burner units on the carrier 35 are chosen in such a manner that the hood 29 may be shifted vertically on the bar 31 and inserted between each pair of burner units for cooperation with the next lower unit.

The plastic bag 34 on a pallet 32 is tightened about the stacked goods 33 by heat-shrinkage brought about by the apparatus of FIG. 1 or FIG. 3 in a closely similar manner. The carriage 8 of either apparatus is moved in an approximately circular path about the pallet while the operator controls the several heating units by means of the switches 16, 17, and the non-illustrated ignition switch on the panel 12.

The bottom rim of the plastic bag 34 is preferably shrunk first so as to anchor the bag below the bottom of the loading platform. For this purpose, the apparatus of FIG. 1 may be guided about the pallet 32 while hot combustion gases are discharged from the burner 4 and the gas supply to the burner unit 5 is shut off. Cool air only is discharged from the unit 5 against the previously softened plastic of the shrunken lower rim to harden the same. The units 3 and 26 discharge combustion gases to shrink the bag 34 about the stacked goods while a vertical shrinkage of the bag which would pull it loose from the pallet 32 is prevented by the simultaneously hardened lower rim. Shrinkage of the top is caused by the auxiliary unit 26 which may be adjusted according to the vertical height of the stack for approximately uniform spacing between the bag 34 and the several burner units.

It is sometimes necessary to load packages on a pallet in a stack which tapers in an upward direction. Adequately uniform spacing of the combustion tube orifices and the plastic bag covering such an approximately pyramidal stack can be achieved by tilting the carrier housing 2 on the shaft 7, and fastening it in the desired angular position by means of the latch 6. However, the temperature of the combustion gases and the velocity imparted to them by the individual blowers of the several units are high enough to achieve the desired heating and shrinking effect on the plastic bag at relatively great distances from the orifices of the combustion tubes without unduly softening the plastic at closer range. Precisely uniform and very close spacing of the tube orifices from the plastic bag thus is not essential to the operation of the apparatus.

When the axes of the combustion tubes are inclined obliquely downward at an angle of approximately 30 to the horizontal, as shown in FIG. 3, the range and effectiveness of a burner unit under otherwise identical conditions is greater than with the horizontal arrangement of FIGS. 1 and 2. This is believed due to the more turbulent, thermal, upward draft of the combustion gases along the plastic bag that is achieved by the oblique burner unit arrangement.

Adequate shrinkage of the plastic sheet material over the top of the stacked goods is achieved by the hood 29 which deflects the rising combustion gases and may be adjusted vertically for differences in height between pallet loads. An additional unit, not shown in FIG. 3, may be paired with the lowermost burner unit 3 in FIG. 3, as at 4 in FIG. 1, but is not required if other measures are taken to prevent upward shrinkage of the bag 34. The carrier 35 may be tilted in the manner described with reference to FIG. 1 for accomodating pyramidal and similar stacks.

The apparatus of FIG. 4 is identical with that of FIG. 3 except for three guide rails 36 on which the two topmost burner units 3 and the lowermost unit 3 may be adjusted longitudinally for more uniform spacing of their burner orifices from a pallet load of irregular shape. The carrier 35 does not require tilting on the associated carriage 8 in the apparatus of FIG. 4, and may thus be fixedly mounted on the carriage.

FIGS. 5 to 7 illustrate apparatus of the invention for tightening a heat-shrinkable plastic sheet about palleted, stacked goods which has been found to combine the ability of expeditiously handling a run of identical pallet loads with the adaptability of the devices shown in FIGS. 1 to 4.

As is best seen in FIG. 6, a turntable 39 is arranged on a fixed base in a gap between two partially illustrated roller conveyors 37, 38, and is equipped with rollers 40 rotatable about horizontal axes which may be aligned parallel with the rollers 40 of the two conveyors. The turntable 39 is equipped with a coaxial pulley 43, and a V-belt 49 drivingly connects the pulley 43 with a corresponding drive pulley 48 on the vertical output shaft of an electric motor 47 mounted on the conveyor 38 by means of a bracket 41.

Pallet-loads of stacked goods loosely wrapped in plastic bags may be fed sequentially to the turntable 39 by the conveyor 37, turned 180 or 360 with the turntable 39 by the motor 47, and thereafter discharged by the conveyor 38. The turntable 39 is flanked on opposite sides by two heater columns, one column 1 being mounted on acarriage 8, the arrangement being identical with that illustrated in FIGS.1 and/or 2 so as not to require more detailed description.

As is better seen in FIGS. 5 and 7, the other heater column consists of a slab-shaped carrier housing 45 from which five burner units 3 project in vertically offset relationship. The housing 45 may be rotated about a vertical axis, in a manner not specifically shown, on a fixed base 46 whose height is sufficient to bring the lowermost burner unit 3 to the approximate level of the loading platform on a pallet located on the turntable 39, the conveyors 37, 38 being horizontally aligned with the turntable by means of legs 42. The burner units 3 are connected with respective sources of combustible gas and electric current in a non-illustrated conventional manner.

Instead of the carriage 8 being guided in an approximate circle about a pallet, as described with reference to FIGS. 1-4, the pallet 32 on the platform 39 is turned relative to the suitably adjusted, stationary burner units 3. During rotation of the turntable, the vertical edges of the stack of goods 33 and the corresponding portions of the plastic bag 34 move closer to the burner orifices than the surfaces of the stack and bag intermediate the edges. The resulting small difference in the temperature of the combustion gases impinging on the edge portions and the flat portions respectively of the bag is adequately compensated for by the higher linear speed of the edge portions which are farther removed from the vertical axis of rotation of the turntable 39. Reasonable care should be taken to center the load on the turntable.

If both heater columns are operated, a pallet 32 on the turntable 39 need be turned only 180 for complete shrinkage of the associated plastic bag 34. The column 1, however, is readily moved elsewhere when needed for shrinking a plastic envelope on palleted goods arranged in a stack for which the conveyor line is not set, and continuous operation of the apparatus otherwise shown in FIG. 6 may be maintained without the column 1 if each pallet is turned 360. Limit switches on the turntable, not shown, may be set for stopping the motor 47 after a full turn or half a turn of the pallet. The motor may be started by an operator or automatically by another limit switch on the turntable 39 responding to the proper positioning of a pallet in a manner well known in itself. The effective spacing of the burner units on the carrier 45 from the palleted load may be varied by turning the carrier about its vertical axis. The burner units on the carrier 45 may be oriented and adjustable in the manner shown in FIG. 4.

The apparatus of FIG. 6 lends itself readily to fully automatic operation in an obvious manner not itself relevant to this invention, and the control panel on the carriage 8 for the column 1 in FIG. 1 may be plugged into a programming device which ignites and extinguishes the gas in the burner units on the base 46 in timed sequence with operation of the turntable.

Other changes in the illustrated embodiments will readily suggest themselves to those skilled in the art. A

portable apparatus of the type illustrated in FIGS. 1 to 4 is preferably battery operated to avoid the need for a trailing power cable. If the same apparatus is also intended for temporary operation in a conveyor line for increasing the output of the latter, as is shown in FIG. 6, it is preferably equipped with a transformer and suitable switching gear which permits alternative operation by line current. In any event, a battery charger should be installed on the carriage 8 for recharging the batter 14 during idle periods of the apparatus, as is customary in fork lifts and similar electrically operated industrial vehicles.

It should be understood, therefore, that the foregoing disclosure relates only to preferred embodiments of the invention, and that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purpose of the disclosure which do not constitute departures from the spirit and scope of the invention set forth in the appended claims.

What is claimed is:

1. Apparatus for tightening a heat-shrinkable plastic sheet about stacked goods comprising, in combination:

a. a vertically extending support;

b. a plurality of burner units mounted on said support in vertically offset relationship, each burner unit including 1. a mixing chamber,

2. a combustion tube having an axis, one open axial end, and another axial end communicating with said chamber, the axes of the combustion tubes of said burner units extending substantially in a common direction,

3. motor-driven blow means for blowing atmospheric air into said mixing chamber, and

4. igniting means for igniting said gas in said chamber; and

c. a source of a combustible gas communicating with said mixing chamber.

2. Apparatus as set forth in claim 1, wherein said axes are inclined 30 i 10 relative to the horizontal, said open end of each tube being downwardly offset from the other axial end.

3. Apparatus as set forth in claim 2, further comprising guide means on said support for guiding movement of at least one of said units in said common direction.

4. Apparatus as set forth in claim 1, a downwardly open hood member mounted on said support above the open end of the combustion tube in one of said burner units.

5. Apparatus as set forth in claim 4, further comprising guide means on said support for vertically guiding said hood member.

6. Apparatus as set forth in claim 1, wherein said source of combustible gas includes a container for holding said gas, a conduit connecting said container to each of said burner units, a control valve in each of said conduits, and control means for individually opening and closing said valves.

7. Apparatus as set forth in claim 1, further comprising a wheeled carriage, said support and said source of combustible gas being mounted on said carriage.

8. Apparatus as set forth in claim 7, further comprising a plurality of electric motors drivingly connected with respective ones of said blower means, an electric storage battery mounted on said carriage, and conductive means for connecting said battery to each of said motors.

9. Apparatus as set forth in claim 1, further comprising a base, a pivot securing said support to said base for pivoting movement about a pivot axis transverse to said common direction.

10. Apparatus as set forth in claim 1, further comprising a turntable adapted to hold said stacked goods, said common direction having a horizontal component, and said turntable being offset from said support in the direction of said horizontal component.

11. A method of tightening a sheet of heat-shrinkable plastic about goods loosely enveloped by said sheet which comprises wheeling the apparatus defined in claim 7 about said enveloped goods while burning said gas with said atmospheric air in each of said combustion tubes, and discharging the hot combustion gases so produced against said sheet. 

1. Apparatus for tightening a heat-shrinkable plastic sheet about stacked goods comprising, in combination: a. a vertically extending support; b. a plurality of burner units mounted on said support in vertically offset relationship, each burner unit including
 1. a mixing chamber,
 2. a combustion tube having an axis, one open axial end, and another axial end communicating with said chamber, the axes of the combustion tubes of said burner units extending substantially in a common direction,
 3. motor-driven blow means for blowing atmospheric air into said mixing chamber, and
 4. igniting means for igniting said gas in said chamber; and c. a source of a combustible gas communicating with said mixing chamber.
 2. a combustion tube having an axis, one open axial end, and another axial end communicating with said chamber, the axes of the combustion tubes of said burner units extending substantially in a common direction,
 2. Apparatus as set forth in claim 1, wherein said axes are inclined 30* + or - 10* relative to the horizontal, said open end of each tube being downwardly offset from the other axial end.
 3. Apparatus as set forth in claim 2, further comprising guide means on said support for guiding movement of at least one of said units in said common direction.
 3. motor-driven blow means for blowing atmospheric air into said mixing chamber, and
 4. igniting means for igniting said gas in said chamber; and c. a source of a combustible gas communicating with said mixing chamber.
 4. Apparatus as set forth in claim 1, a downwardly open hood member mounted on said support above the open end of the combustion tube in one of said burner units.
 5. Apparatus as set forth in claim 4, further comprising guide means on said support for vertically guiding said hood member.
 6. Apparatus as set forth in claim 1, wherein said source of combustible gas includes a container for holding said gas, a conduit connecting said container to each of said burner units, a control valve in each of said conduits, and control means for individually opening and closing said valves.
 7. Apparatus as set forth in claim 1, further comprising a wheeled carriage, said support and said source of combustible gas being mounted on said carriage.
 8. Apparatus as set forth in claim 7, further comprising a plurality of electric motors drivingly connected with respective ones of said blower means, an electric storage battery mounted on said carriage, and conductive means for connecting said battery to each of said motors.
 9. Apparatus as set forth in claim 1, further comprising a base, a pivot securing said support to said base for pivoting movement about a pivot axis transverse to said common direction.
 10. Apparatus as set forth in claim 1, further comprising a turntable adapted to hold said stacked goods, said common direction having a horizontal component, and said turntable being offset from said support in the direction of said horizontal component.
 11. A method of tightening a sheet of heat-shrinkable plastic about goods loosely enveloped by said sheet which comprises wheeling the apparatus defined in claim 7 about said enveloped goods while burning said gas with said atmospheric air in each of said combustion tubes, and discharging the hot combustion gases so produced against said sheet. 